-LRB- CNN -RRB- -- A silent , invisible battle is being fought against roadside bombs in Iraq . Though the military does n't like to advertise their use , electronic jamming systems are playing a key role in neutralizing the threat .

Smoke billows from tires of a U.S. military truck hit by an IED near the Iraqi-Syrian border in October 2005 .

`` Any weapon we had against IEDs , -LSB- improvised explosive devices -RSB- was utilized including jamming technology , '' said Jason Spencer , 29 , an Oklahoma City , Oklahoma , engineer who served with the Army in Iraq in 2005 .

Vehicle mounted electronic jammers attempt to block a signal going to a radio-controlled IED . The military also uses portable backpack jammers .

`` The sophistication of IEDs definitely increased during my time in Iraq , '' said Spencer . `` There was a definite increase in remote detonation . ''

A signal going to a remote-controlled IED operates on a radio or infrared frequency .

Jamming devices , known as Counter Radio Controlled Improvised Explosive Device Electronic Warfare , or CREW systems , attempt to intercept or block a signal before it reaches its intended target , preventing detonation .

One common method is barrage jamming , which knocks out a broad range of radio signals . However , it also knocks out communications used by U.S. troops putting them at increased risk .

`` Ideally what you want to be able to do is have something that can grab very precise signals , capture the signals and render them irrelevant without knocking out your own communication , '' said CNN military analyst retired Army Brig. Gen. James `` Spider '' Marks .

These technologies represent the last line of defense , Marks said . `` We do n't want to give our potential enemies an understanding of what we are doing to counter their efforts , '' he said .

Along with jammers , troops use air surveillance , robots , blast-resistant vehicles and mine rollers as countermeasures . See counter-IED technologies in Iraq ''

IEDs are the No. 1 source of U.S. and alllied casualties in Iraq , according to the Department of Defense . From July 2003 to July 2007 , 1,565 coalition forces were killed by IEDs , according to iCasualties.org . See the casualty toll inflicted by IEDs ''

`` We dealt with hundreds of IEDs while in theater , '' said Spencer . `` IEDs were always on our minds during every patrol . ''

Spencer says IEDs come in a variety of shapes and sizes . `` From a simple mortar round on the side of the road with a fuse and a wire running to a push-button , to complex explosives poured into concrete -LRB- shaped like curbs -RRB- with remote detonators and booby traps . ''

Most roadside bombs are remotely detonated using common household devices : cell phones , garage door openers , burglar alarms , key fobs , doorbells , or remote controls for toy cars . Learn more about the IED threat ''

`` Our enemy hides in plain sight . He buys his bomb parts in stores . It 's standard commerce , '' said Marks .

U.S. forces are dealing with an adaptive , innovative and flexible enemy , according to the Joint Improvised Explosive Device Defeat Organization , or JIEDDO , which is leading the counter-IED effort for the military .

As insurgents modify their devices to outwit the military , the military in turn adapts its own jamming technologies .

Many companies have been tapped to supply jammers to coalition forces . JIEDDO is interested in technologies that can be used in the field within two to eight months -- `` light speed '' in Defense Department terms .

The Army 's main CREW system is the Warlock Duke , a vehicle - mounted radio jammer developed by Syracuse Research Corporation . It 's capable of jamming most radio-controlled IEDs , according to the Pentagon .

The Navy , which oversees the CREW program , contracted BAE Systems to produce 3,800 wearable jammers to be fielded in Afghanistan and Iraq in 2008 .

Canadian firm Med-Eng is building jammers for the Marines , reports military contractor General Dynamics .

By the end of 2007 , JIEDDO will have funded more than 30,000 jammers for Marine and Army units . They have spent $ 1.6 billion on jamming technology for this fiscal year .

`` This gear saves lives every day , '' wrote retired Gen. Montgomery Meigs , director of the Joint IED Defeat Organization , in a column titled `` On the Offensive : The Battle Against IEDs . ''

One in six IEDs causes casualties in Iraq , JIEDDO reports . To remain effective the enemy `` must expose himself more and take higher risks to do his ugly work , '' Meigs said .

In January , the Government Accounting Office launched a review of JIEDDO and its efforts to counter IEDs . The Defense Science Board criticized the agency for focusing too much on defensive countermeasures `` to which the enemy quickly adapts , making these efforts less effective , '' in an April 2006 report .

JIEDDO is fully cooperating with the GAO , said Col. Dewey Ford , director of strategic communications for JIEDDO . He added that Congress has long supported eliminating the IED threat .

JIEDDO said it is aggressively going after the bomb makers , working to destroy their networks . The agency acknowledges that the mission wo n't be achieved merely by technical means .

`` The best way to counter the IED threat is through understanding the network that allows an IED to even be assembled , '' said Marks , who supports JIEDDO 's work .

`` I 'd rather have the guy who is going to put that IED in place get killed long before he 's even part of the network . And I do n't want him to know how I found him out because I want to find out where all his buddies are and kill them too . '' E-mail to a friend

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Counter-IED technologies are troops ' last line of defense in Iraq

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Signal jammers used to block an IED from detonating

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Enemy is adaptive , innovative and flexible

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Best way to combat insurgents -- go after the bomb makers